Between March and July, Cook, 17, tried to recruit someone to conduct the shooting on Nov. 11, 2011 — 11/11/11 — according to his arrest affidavit. The teen, who attended Leto High last year, threatened to blow up the school, authorities said.

On Monday, a day before classes began for the academic year, deputies arrested Cook at his Town 'N Country home. He faces adult charges of solicitation to commit murder and threatening to discharge a destructive device. Authorities did not speculate on a motive.

Cook's mother, Dawn Hicks, 49, said she is shocked at the charges. She said she never heard her son talk about shooting anyone. Several friends said they remember him making off-handed comments, but they thought he was joking.

"This is nothing to joke about. You can't yell 'bomb' on an airplane," said sheriff's Deputy Larry McKinnon. "You have to be accountable for your behavior."

The investigation started in July, when Crime Stoppers received an ominous tip: Someone was planning a mass shooting at Leto High, a school of nearly 1,800 students near Sligh and Manhattan avenues in Tampa. A specific day and time had been picked, the tipster said.

Deputies interviewed witnesses and gathered information. The tip seemed valid, so they went to the suspect's house.

Hicks said she let deputies search her son's room last week.

"I said 'yes' because I knew that Austin would never be involved in anything like this," she said. Now she wishes she had waited until investigators had obtained a search warrant.

Deputies seized a .22-caliber rifle, bow and arrow and several books about firearms. Hicks said the rifle is an heirloompassed on to her son from his grandfather.

"It hadn't been fired in more than 40 years," she said.

The books simply reflected an interest in guns, she said. He was considering joining the military after he got his GED, she said. His friends say he was acting in a war-style movie that one of them — a local film student — was directing.

Investigators say the computer contained a Columbine video game and showed Cook had made multiple inquiries about Columbine and Virginia Tech.

The 1999 attack at Columbine High in Colorado claimed 12 students and a teacher; the 2007 attack at Virginia Polytechnic Institute killed 32 people.

Cook's arrest affidavit also said he had inquired about gun shows in Tampa.

After Cook's arrest, he denied to authorities the accusation, but said he had joked about it with a friend.

He was initially booked into a juvenile facility. The family didn't learn he was facing adult charges until he called his mother Tuesday.

Hicks said her son was arrested last year at school for marijuana possession and was supposed to go through a first-time offender program. But then in April, he "busted up some cars," slashing their tires and breaking their windshields, she said. He was put on probation and was going to do community service, she said.

"His curfew was 10 o'clock," she said. "And he was on time every day, at 10 o'clock."

She said he had failed his Florida Comprehensive Assessment Test but was going to get his GED at Leto, she said. Then, he was planning to go to Hillsborough Community College or join the military.

School district spokesman Steve Hegarty said school officials told Cook several weeks before his arrest that he would not be allowed to return to Leto.

"He wasn't going to return once we found out about these charges," Hegarty said.

According to the arrest report, Cook is a member of a gang called the "Anonymous Goons." His mother says that was the name a group of his friends gave themselves. It wasn't a criminal gang, she said.

On his MySpace page, Cook quotes slightly altered lyrics from a new song called Another Way to Die by the hard rock band Disturbed: "The time bomb is ticking, and no one is listening, my future is fading, is there any hope I'll survive?"

The band's website suggests the song is about global warming.

Hicks said her son wasn't suicidal and that she checked his MySpace and Facebook pages regularly. She never saw anything that caused her alarm.

On his MySpace page, he lists his occupation as "outlaw." He says he likes rock, metal and reggae music and war stories and survival guides. His hero is Bob Marley.

Hegarty said the school district regularly investigates rumors about violence and communicates with law enforcement.

Most of the time, "rumors are rumors," Hegarty said. He said for charges like these to be filed, the allegations must be serious.

"I think it sends a clear message that you shouldn't say things like that," he said.

Times news researcher John Martin and staff writers Colleen Jenkins, Robbyn Mitchell, Tom Marshall and Danny Valentine contributed to this report. Jessica Vander Velde can be reached at jvandervelde@sptimes.com or (813) 226-3433.

There is a reason why the air in Tampa Bay is filled with playoff talk. If Thursday night's 12-8 Bucs preseason win over the Jaguars is any indication, it's also going to be filled with footballs thrown by quarterback Jameis Winston.